Failure detection device for hydraulic motor and hydraulic drive vehicle

ABSTRACT

A failure detection device for a hydraulic motor according to the present invention comprises a hydraulic pump  3  that is driven by a prime mover  2 ; a hydraulic motor  1  for traveling that is driven by hydraulic oil discharged from the hydraulic pump  3 ; a transmission  7  that is connected with an output shaft of the hydraulic motor  1  for traveling; a stopping detection device  26  that detects that a traveling vehicle has stopped; a fluid level detection device  35  that detects an oil level in the transmission  7 ; and a warning device  39, 40  that issues a warning when the stopping detection device  26  detects that the traveling vehicle has stopped, and also the fluid level detection device  35  detects that the oil level in the transmission  7  has reached a predetermined value La.

TECHNICAL FIELD

This invention relates to a device that detects a failure of thehydraulic motor installed in the hydraulic drive vehicle such as awheeled hydraulic excavator.

BACKGROUND ART

Generally, the hydraulic drive vehicle such as a wheeled hydraulicexcavator comprises a hydraulic pump and a hydraulic motor fortravelling which is driven by oil discharged from the hydraulic pump.The output shaft of this hydraulic motor is connected with the inputshaft of the transmission, and the rotation of the hydraulic motor istransmitted to the wheels through the transmission. A drain chamber isprovided to the hydraulic motor, and the drain oil from the hydraulicmotor returns to a reservoir via the drain chamber. A seal member isprovided between the drain chamber of the motor and a transmissionchamber of the transmission, in order to prevent the drain oil fromflowing into the transmission chamber from the drain chamber.

In such a hydraulic drive vehicle as described above, if a foreign bodyshould be ingested by the hydraulic motor, proper operation of thehydraulic motor is impeded and there is a danger that the hydraulicmotor may be damaged. If the hydraulic motor is damaged, a copious flowof the discharged oil from the hydraulic pump flows into the drainchamber and then flows into the transmission chamber, penetratingthrough the seal member. As a result, the transmission chamber is filledwith the drain oil, and a great resistance comes to act on thetransmission so that the travelling performance of the vehicledeteriorates. Moreover, when transmission oil becomes mixed with thedrain oil, the quality of the mission oil may be deteriorated, and thismay exert a negative influence upon the operation of the transmission.

DISCLOSURE OF THE INVENTION

The present invention is to provide a failure detection device for ahydraulic motor that is capable of detecting abnormal operation of thehydraulic motor to respond appropriately an abnormal operationalsituation.

Moreover, the present invention is to provide a hydraulic drive vehiclewhich is equipped with such a failure detection device for a hydraulicmotor.

In order to achieve the object described above, a failure detectiondevice for a hydraulic motor according to the present inventioncomprises a hydraulic pump that is driven by a prime mover; a hydraulicmotor for traveling that is driven by hydraulic oil discharged from thehydraulic pump; a transmission that is connected with an output shaft ofthe hydraulic motor for traveling; a stopping detection device thatdetects that a traveling vehicle has stopped; a fluid level detectiondevice that detects an oil level in the transmission; and a warningdevice that issues a warning when the stopping detection device detectsthat the traveling vehicle has stopped, and also the fluid leveldetection device detects that the oil level in the transmission hasreached a predetermined value.

Furthermore, a hydraulic drive vehicle according to the presentinvention comprises a hydraulic pump that is driven by a prime mover; ahydraulic motor for traveling that is driven by hydraulic oil dischargedfrom the hydraulic pump; a transmission that is connected with an outputshaft of the hydraulic motor for traveling; a stopping detection devicethat detects that the vehicle has stopped; a fluid level detectiondevice that detects an oil level in the transmission; and a warningdevice that issues a warning when the stopping detection device detectsthat the vehicle has stopped, and also the fluid level detection devicedetects that the oil level in the transmission has reached apredetermined value.

Therefore, it is possible for an operator to recognize an abnormal stateof the hydraulic motor at an early stage and to take an appropriatecountermeasure to the abnormal state.

It is also acceptable to restrict a driving of the hydraulic motor fortraveling instead of issuing a warning. It is desirable to lower therotational speed of the prime mover when the abnormal state of thetraveling motor has been detected. It is also acceptable to prevent thevehicle from traveling upon detection of the abnormal state. In such anabnormal state, restart of the prime mover may be prevented. Inaddition, a warning may be issued as well.

It is also possible to disable the warning device from issuing thewarning or to disable a drive restriction upon the vehicle, when theworking state has been detected.

It is desirable to cancel the above-described control in response to areset command. An ignition key switch may issue such a reset command.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for ahydraulic motor according to the first embodiment of the presentinvention.

FIG.2 is sectional view of a traveling motor to which the presentinvention has been applied.

FIG. 3 schematically illustrates the details of a controller whichconstitutes the failure detection device according to the firstembodiment of the present invention.

FIG. 4 is a flow chart showing an example of procedure executed by thecontroller.

FIG. 5 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for thehydraulic motor according to the second embodiment of the presentinvention.

FIG. 6 schematically illustrates the details of a controller whichconstitutes the failure detection device according to the secondembodiment of the present invention.

FIG. 7 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for ahydraulic motor according to the third embodiment of the presentinvention.

FIG. 8 schematically illustrates the details of the controller whichconstitutes the failure detection device according to the thirdembodiment of the present invention.

FIG. 9 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for ahydraulic motor according to the fourth embodiment of the presentinvention.

FIG. 10 schematically illustrates the details of the controller whichconstitutes the failure detection device according to the fourthembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment

A wheeled hydraulic excavator that is equipped with a failure detectiondevice according to the first embodiment of the present invention willnow be described with reference to FIGS. 1 through 4. The wheeledhydraulic excavator comprises a wheeled undercarriage upon which anupper-structure is rotatably mounted, and a working attachment is fittedto this upper-structure. A hydraulic motor 1 for traveling which isdriven by a hydraulic circuit for traveling shown in FIG. 1 is providedin the undercarriage.

As shown in FIG. 1, hydraulic oil is discharged from a main pump 3 whichis driven by an engine, the direction and flow rate of the dischargedoil are controlled by a control valve 4, and then the hydraulic oil issupplied to a traveling motor 1 via a brake valve 6 with a built-incounterbalance valve 5. A transmission 7 is connected with an outputshaft la of the traveling motor 1. The rotational speed of the travelingmotor 1 is changed by the transmission 7, and is transmitted to tires 10through propeller shafts 8 and axles 9. Thus, the wheeled hydraulicexcavator is propelled. It should be noted that the pressure oil fromthe main pump 3 is also supplied to a hydraulic circuit for workingwhich is not shown in the figure, and drives actuators for working.

The direction of changeover and operation amount of the control valve 4are controlled by pilot pressure from a pilot control circuit. Thetraveling speed of the vehicle can be controlled by controlling theamount by which the control valve 4 is operated. The pilot controlcircuit comprises a pilot pump 21, a traveling pilot valve 23 thatgenerates a secondary pilot pressure P1 according to the amount by whichan accelerator pedal 22 is stepped upon, a slow-return valve 24 thatdelays oil returning to the pilot valve 23, and a forward/reverseswitchover valve 25 which is used for selecting forward traveling,reverse traveling or neutral for the vehicle. The forward/reverseswitchover valve 25 is constituted of a solenoid-controlled directionalcontrol valve, and its position is changed over by operating a switchnot shown in the figures.

FIG. 1 shows the condition with the forward/reverse switchover valve 25in its neutral (N) position, and moreover when the traveling pilot valve23 is not being operated. Accordingly, the control valve 4 is in itsneutral position, the pressure oil from the main pump 3 returns to areservoir, and the vehicle remains stopped. When the forward/reverseswitchover valve 25 is switched to its forward traveling position (Fposition) or to its reverse traveling position (R position) by theoperation of the switch, and then the accelerator pedal 22 is steppedupon, the secondary pressure P1 according to the amount by which theaccelerator pedal is operated acts on a pilot port of the control valve4. The control valve 4 is operated by the operation amount correspondingto the secondary pilot pressure P1. Thus, the discharged oil from themain pump 3 is led to the traveling motor 1 via the control valve 4, acenter joint 12 and the brake valve 6, so as to drive the travelingmotor 1. At this time, the leakage oil from the traveling motor 1 iscollected to the reservoir through a drain line (drain chamber) 11.

When the accelerator pedal 22 is released during the vehicle traveling,the pressure oil from the pilot pump 21 is interrupted by the travelingpilot valve 23, and its outlet port is connected to the reservoir. As aresult, the pressure oil having acted on the pilot port of control valve4 returns to the reservoir via the forward/backward switchover valve 25,the slow-return valve 24 and the traveling pilot valve 23. At this time,the returning oil flow is restricted by the restriction of the slowreturn valve 24, so that the control valve 4 returns to its neutralposition gradually. When the control valve 4 returns to its neutralposition, the supply of the pressure oil (drive pressure) isinterrupted, and the counterbalance valve 5 is then switched to itsneutral position as shown in FIG. 1.

At this time, the vehicle continues to progress due to its inertiaforce, and the operation of the traveling motor 1 changes over frommotor action to pump action, in which its B port is its suction (inlet)port and its A port is its discharge (outlet) port in FIG. 1. Flow ofthe pressure oil from the traveling motor 1 is restricted by therestriction of the counterbalance valve 5 (neutral restriction), thepressure between the counterbalance valve 5 and the traveling motor 1then rises and acts on the traveling motor 1 as brake pressure. As aresult, the traveling motor 1 generates the brake torque to slow thevehicle down. If, during the pump operation, the quantity of oil flowinginto the traveling motor 1 becomes insufficient, the additional oil issupplied from a make-up port 13 thereto. The maximum brake pressure isregulated by relief valves 14 and 15.

A governor 2 a of the engine 2 is connected with a pulse motor 32 via alink mechanism 31, and the rotational speed of engine 2 is controlled byrotation of the pulse motor 32. In particular, the engine speed isincreased by the normal rotation of the pulse motor 32, while it isdecreased by the reverse rotation of the pulse motor. A potentiometer 33is connected with the governor 2 a via the link mechanism 31, and thispotentiometer 33 detects a governor lever angle corresponding to therotational speed of the engine 2. The detected value is input to thecontroller 30 as a control rotational speed NO.

Furthermore, the controller 30 is connected with a speed sensor 26 thatdetects the vehicle speed, a pressure sensor 34 that detects thesecondary pilot pressure P1 generated by the traveling pilot valve 23corresponding to the pedal operation amount, a fluid level sensor 35that detects the oil level in the transmission 7, a reset switch 36, andan ignition key switch 37 that is turned on/off according to theoperation of an ignition key, respectively. The fluid level sensor 35 isa limit switch, the limit switch 35 is turned on by a float 35 a whenthe oil level in the transmission reaches a predetermined value La whichis set in advance.

A power source 38 is connected with the key switch 37, and theelectrical power is supplied to the controller 30 in response to the keyswitch 37 being turned on. Accordingly, the controller 30 implementscalculations as will be described later, to control the rotation of thepulse motor 32 by outputting the control signal to the pulse motor 32and also to control operations of a buzzer 39 and a warning lamp 40(which together are referred to as a warning device) by outputtingcontrol signals thereto.

Next, the construction of the traveling motor 1 will be explained. FIG.2 is a sectional view of the variable displacement traveling motor 1. Asshown in FIG. 2, a plurality of pistons 42 (only one of which is shownin the figure) are connected with a flange 41 of the output shaft la ofthe traveling motor 1, along its circumferential direction. The pistons42 are slidably inserted into oil chambers 43 a formed in a cylinderblock 43 through piston rings 42 a. The end of the cylinder block 43comes into contact with a swash plate 44, and their contacting surfacesmutually define a circular cone shape. The swash plate 44 can be swungor inclined together with the cylinder block 43 in the direction of thearrow shown in the figure, and the motor displacement varies accordingto the swing amount or inclined angle of the swash plate.

An inlet or suction port and an outlet or delivery port of oil, notshown in the figure, are provided in the swash plate and a motor cover45 which is in contact with the swash plate 44, the suction port and thedelivery port extending over half a phase, respectively. And, thepressure oil from main pump 3 flows into the oil chambers 43 a throughthe suction port, while the oil from the oil chambers 43 a flows out tothe reservoir through the delivery port. Due to this, the pistons 42 areslid within the oil chambers 43 a, and, while the swash plate 44 is keptin contact with the cylinder block 43, the output shaft la of the motor1 rotates as a unit with the cylinder block 43 and the pistons 42. Aninput shaft 7 a of the transmission 7 is connected by splines with themotor output shaft 1 a so that the rotation of the traveling motor 1 istransmitted to the transmission 7.

At this time, portions of the pressure oil which is supplied to the oilchambers 43 a from the main pump 3 leaks into the drain chamber 11through gaps between the mutually contacting surfaces of the swash plate44 and the cylinder block 43, or gaps between the mutually slidingsurfaces of the pistons 42 and the oil chambers 43 a. This leakage oilreturns to the reservoir via a drain hole 1 a which is provided in thebottom of the motor casing 46, while the oil is prevented from flowinginto the transmission chamber 7 b from the drain chamber 11 by sealrings SR.

If, at this time, a foreign body, for example, should get into themutually sliding surfaces of one of the pistons 42 and causes the piston42 to stick in (to contact directly with) the cylinder block 43, thecylinder block 43 rotates while being dragged by the piston 42 and then,the gap between the cylinder block 43 and the swash plate 44 becomespartially increased. Moreover, according to circumstances, the pistonring 42 a may be damaged, which causes the gap between the mutuallysliding surfaces to become wider. As a result, a large quantity of thepressure oil from the main pump 3 flows into the drain chamber 11through these gaps, and the oil in the drain chamber 11 may penetratethrough the seal rings SR to flow into the transmission chamber 7 b. Ifthis happens, the oil level in the transmission chamber 7 b rises, andthe resistance that acts on the driving shaft of the transmission 7 mayincrease, as well as the performance of the transmission oil maydeteriorate, which exerts a negative effect on the operation of thetransmission 7.

In this embodiment, this type of abnormal operation of the travelingmotor 1 is detected with a vehicle speed sensor 26 and a fluid levelsensor 35, and such abnormal state is responded as follows.

FIG. 3 is a schematic illustration to explain details of the controller30. When the ignition key switch 37 is turned on, the electric power issupplied to the controller 30 to start execution of its processing. Afunction generator 301 outputs a set signal to a set terminal S of a RSflip-flop 302 when the fluid level sensor 35 is switched on, that is,when the oil level in the transmission chamber 7 b is equal to orgreater than the predetermined value La. The value La, in this case, isset to correspond to rise of the oil level due to the breakdown of themotor 1, as described above, so that when the oil level reaches thevalue La, it may be determined that the traveling motor 1 has brokendown.

When the set signal is input to the set terminal S of the flip-flop 302,the flip-flop 302 outputs a high-level signal from its terminal Q tochange over a switchover circuit 303 to its contact “a” side. When thevehicle speed detected by the speed sensor 26 is equal to or lower thana predetermined value (which may equal zero), in other words, when thevehicle has stopped, a function generator 308 outputs a close signal toclose a changeover switch 309. As a result, electrical power is suppliedto a buzzer 39 and a warning lamp 40, so that the buzzer emits sound andthe warning lamp 40 is illuminated.

When a reset switch 36 is turned on, the reset switch 36 outputs are setsignal to a reset terminal R of the flip-flop 302. The flip-flop 302sets low-level in the terminal Q in response to this reset signal, andthe switchover circuit 303 is then switched to its contact “b” side. Asa result, the supply of electrical power to the buzzer 39 and thewarning lamp 40 is interrupted so that the buzzer sound is brought to ahalt and the warning lamp 40 is extinguished. And, when it is detectedby the speed sensor 26 that the vehicle is traveling, an open signal isoutput to the changeover switch 309 to open the changeover switch 309.Also in this case, the buzzer sound is stopped, and the warning lamp 40is turned off.

A function by which the engine speed should increase along with increaseof the traveling pilot pressure is set in advance in the functiongenerator 304, as schematically shown in the figure. The functiongenerator 304 sets the rotational speed N corresponding to the detectedvalue P1 from the pressure sensor 34 based upon this function, andoutputs this set value N to a switchover circuit 305. When theswitchover circuit 303 is switched to its contact “a” side and also thechangeover switch 309 is closed, the switchover circuit 305 is switchedto its contact “a” side. On the other hand, when the switchover circuit303 is switched to its contact “b” side and also the changeover switch309 is open, the switchover circuit 305 is switched to its contact “b”side. Accordingly, the switchover circuit 305 selects either therotational speed N as set by the function generator 304 or an idlingrotational speed Ni which is set in advance in a rotational speedsetting device 306, and outputs its selected rotational speed to a servocontrol section 307 as a target rotational speed Ny. In the servocontrol section 307, the target rotational speed Ny is compared with thecontrol rotational speed Nθ which corresponds to the amount ofdisplacement of the governor lever as detected by the potentiometer 33,and the pulse motor 32 is controlled so as to bring the controlrotational speed Nθ to match the target rotational speed Ny, accordingto the procedure shown in FIG. 4.

Referring to FIG. 4, first in step S21, the rotational speed commandvalue Ny and the control rotational speed Nθ are read in, and then theflow of control proceeds to step S22. In step S22, Ny is subtracted fromNθ and the result of this subtraction, i.e. the rotational speeddifferential A, is stored in a memory. In step S23, using apredetermined standard rotational speed differential K set in advance,it makes a decision as to whether or not |A|≧K. If an affirmativedecision is made, the flow of control proceeds to step S24 in which adecision is made as to whether or not the rotational speed differentialA>0. If A>0, it implies that the control rotational speed Nθ is greaterthan the rotational speed command value Ny, in other words, the controlrotational speed is higher than the target rotational speed, the flow ofcontrol then proceeds to step S25 in which a signal for instructingreverse rotation of the motor is output to the pulse motor 32 in orderto reduce the engine speed. As a result, the pulse motor 32 is caused torotate in reverse so that the rotational speed of the engine 2 drops.

On the other hand, if A≦0, it implies that the control rotational speedNθ is lower than the rotational speed command value Ny, that is, thecontrol rotational speed is lower than the target rotational value, asignal for instructing normal rotation of the motor is output in orderto increase the engine speed, in step S26. As a result, the pulse motor32 performs normal rotation to increase the engine speed. If a negativedecision is made in step S23, the flow of control proceeds to step S27to output a motor stop signal. Therefore, the rotational speed of theengine 2 is maintained constant. After the appropriate one of the stepsS25–S27 has been executed, the flow of control returns to the beginningof this flow chart.

The outstanding features of the operation of this failure detectiondevice for a hydraulic drive vehicle constructed as described above willnow be explained in concrete term.

(1) During Normal Operation of the Traveling Motor

When the traveling motor 1 is in the normal operating condition, thereis substantially no oil flow from the drain chamber to the transmissionchamber 7 b, and the oil level in the transmission chamber 7 b remainsequal to or less than the predefined value La while vehicle is stopped.Therefore, the switchover circuit 303 and the switchover circuit 305 ofthe controller 30 are switched to their contact “b” side, respectively.In this condition, if the forward/backward switchover valve 25 isswitched to forward traveling or to reverse traveling, and also theaccelerator pedal 22 is stepped upon, the traveling pilot pressure P1 isgenerated in correspondence to the amount by which the accelerator pedalis operated. The servo control section 307 compares the targetrotational speed Ny according to this traveling pilot pressure P1 withthe control rotational speed Nθ corresponding to the detected value fromthe potentiometer 33, and then controls the pulse motor 32 to bring bothrotational speeds to correspond to each other. Therefore, the vehicle ispropelled with its engine speed increasing in line with the increase ofthe amount of pedal operation.

While the vehicle travels, if the oil in the transmission chamber 7 b ischurned up by the rotation of the drive shaft of the transmission 7, thefluid level sensor 35 may be switched on due to change of the oil level.Although the switchover circuit 303 is switched to its contact “a” sidein response to operation of the fluid level sensor, the warning devices39 and 40 will not operate because the changeover switch 309 is open.

(2) When Operation of the Traveling Motor Becomes Abnormal

If the motor piston 42 should get stuck at its sliding portion, by aforeign body having gotten into the sliding portion, a large quantity ofdelivery oil from the hydraulic pump 3 may flow into the drain chamber11 as described above. And, if some of this drain oil should flow intothe transmission chamber 7 b penetrating past or through the seal ringsSR and the oil level in the transmission chamber 7 b should reach thepredefined value La, the function generator 301 outputs the set signalto the set terminal of the flip-flop 302 so that the switchover circuit303 is switched to its contact “a” side in response to a high levelsignal output from the Q terminal of the flip-flop 302. When the vehiclestops under this condition, the changeover switch 309 is closed so thatwarning lamp 40 is illuminated, as well as the buzzer sound beingemitted. Accordingly, the operator becomes aware of an abnormal state ofthe traveling motor 1, and is able to perform an appropriate operation,e.g. to stop the engine, in response to such abnormal state of the motor1.

At this time, the switchover circuit 305 is switched to the contact “a”side. Due to this, the engine speed is lowered to its idling rotationalspeed Ni, and the motor rotational speed also drops in line withreduction in amount of the delivery oil from the pump. As a result, thequantity of oil flow into the drain chamber 11 decreases, so that itbecomes possible to minimize the leakage of oil from the drain chamber11 to the transmission chamber 7 b. Moreover, useless consumption offuel can be prevented. It should be understood that the oil collected inthe transmission chamber 7 b can be exhausted through a drain hole notshown in the figures, and thereby it is possible to regulate the oillevel in the transmission chamber 7 b within the predetermined value.

In the state in which the oil level in the transmission chamber 7 b isbelow the predetermined value La, when the reset switch 36 is operated,the terminal Q of the flip-flop 302 is set to low level and then theswitchover circuits 303 and 305 are switched to their contacts “b” side,respectively. Due to this, the buzzer sound is stopped and also thewarning lamp 40 is extinguished. Moreover, it becomes again possible tocontrol the engine speed in accordance with operation of the acceleratorpedal. As a result, when the vehicle is to be transported upon a trailerfor the repair of the traveling motor 1, it is possible to load thevehicle onto the trailer by driving it under its own power. It should beunderstood that, instead of operating the reset switch 36, it would alsobe acceptable to turn off the ignition key switch 37. If the travelingmotor 1 is damaged heavily and driving the vehicle under its own poweris difficult or impossible, it may be pulled up on the trailer byengaging the end of a bucket of the hydraulic excavator with part of thetrailer and then actuating hydraulic cylinders for a boom or arm.

According to the first embodiment as described above, a failure of thetraveling motor 1 is detected when the oil level in the transmissionchamber 7 b has reached the predetermined value La while the vehiclestops, and then the warning devices 39 and 40 are caused to operate.Therefore, it is possible for an operator to be made aware of abnormaloperation of the traveling motor 1 at an early stage, and to respondappropriately to such abnormal circumstances. In this case, if a periodof time is required before the oil level becomes steady, it may bepossible to detect a failure of the traveling motor 1 based on the valuedetected by the fluid level sensor 35 after such a period of time.

Moreover, the engine speed is lowered to the idling rotation speed Ni torestrict the drive of the traveling motor 1 when a breakdown of themotor 1 is detected. Therefore, the quantity of oil flow into the drainchamber 11 is reduced irrespective of operation amount of theaccelerator pedal 22, and it is possible to prevent oil leakage into thetransmission chamber 7 b. In addition, the warning devices 39 and 40continue to be operated and the restriction upon traveling of thevehicle is maintained until the reset switch 36 is actuated or theignition key switch 37 is turned off when the oil level in thetransmission chamber 7 b has dropped to the predefined value La orlower. Therefore, it is possible that an operator is reliably made awareof the abnormal operation in the traveling motor 1. In addition, whenthe restriction upon the traveling of the vehicle has been cancelled,the engine speed can again be increased according to the operation ofthe accelerator pedal and it is possible to load the vehicle upon thetrailer or the like easily.

Second Embodiment

While, in the first embodiment, the engine speed is lowered to theidling rotational speed Ni to restrict the vehicle speed during afailure in the traveling motor 1, the vehicle will be prohibited fromtraveling, in the second embodiment. The second embodiment of thepresent invention will now be explained with reference to FIGS. 5 and 6.FIG. 5 is a circuit diagram showing the structure of a wheeled hydraulicexcavator which is equipped with a failure detection device according tothe second embodiment, and FIG. 6 schematically illustrates details of acontroller 30A according to the second embodiment. It should be notedthat the same reference numerals are used for elements similar to thatof FIGS. 1 and 3, and the explanation will focus on the points differenttherefrom.

As shown in FIG. 5, the line between the traveling pilot valve 23 andthe slow-return valve 24 can be connected with the reservoir through asolenoid valve 47. The solenoid valve 47 is controlled by a controlsignal from the controller 30A. As shown in FIG. 6, a solenoid 47a ofthe solenoid valve 47 is connected with the changeover switch 309.

While the vehicle is stationary, in other words, while the changeoverswitch 309 is closed, if the switchover circuit 303 is switched to thecontact “a” side due to a failure of the traveling motor 1, the solenoid47 a is excited to switch the solenoid valve 47 to its position B. As aresult, the pressure oil having acted on the pilot port of control valve4 returns to the reservoir via the forward/backward switchover valve 25,the slow return valve 24 and the solenoid valve 47, and the controlvalve 4 is driven back to its neutral position. As a result, the supplyof pressure oil to the traveling motor 1 is intercepted, and even if theaccelerator pedal 22 is actuated, the vehicle stationary state ismaintained. In addition, the warning devices 39 and 40 operate, and theengine speed is limited to the idling rotational speed Ni.

If, in such condition, the reset switch 36 is actuated, the switchovercircuit 303 and 305 are switched to the contact “b” side, respectively.Accordingly, the solenoid 47 a is demagnetized, and the solenoid valve47 is switched to its position A. As a result, the traveling pilotpressure corresponding to the operation of the accelerator pedal is madeto act on the pilot port of the control valve 4, and the supply of thepressure oil to the traveling motor 1 becomes possible.

According to the second embodiment as described above, when a failure inthe traveling motor 1 is detected, the traveling pilot pressure is madeto return to the reservoir by the operation of the solenoid valve 47.Therefore, even if the accelerator pedal 22 is actuated, the travelingmotor 1 continues to be prevented from rotating, and thereafter it ispossible to prevent further oil leakage into the drain chamber 11.

It should be noted that it would also be acceptable to additionallyoperate a brake, such as a parking brake. In this manner, it would bepossible to ensure the stationary state of the vehicle. Moreover, itwould also be acceptable to control the engine speed according to thevalue corresponding to the traveling pilot pressure, instead of limitingthe engine speed to the idling rotational speed Ni. In this case, theswitchover circuit 305 would become unnecessary.

Third Embodiment

While, in the first embodiment, the engine speed is lowered to theidling rotational speed Ni to restrict the vehicle speed during afailure in the traveling motor 1, in addition to this function, theengine 2 is prohibited from restarting, in the third embodiment. Thethird embodiment of the present invention will now be explained withreference to FIGS. 7 and 8. FIG. 7 is a circuit diagram showing theconstruction of a wheeled hydraulic excavator which is equipped with afailure detection device according to the third embodiment, and FIG. 8schematically illustrates the structure of a controller 30B according tothe third embodiment. It should be noted the same reference numerals areused for elements similar to that of the FIGS. 1 and 3, and theexplanation will focus upon the points different therefrom.

As shown in FIG. 7, a starting motor 48 is connected with the controller30B, and the drive of the starting motor 48 is controlled thereby. Asshown in FIG. 8, the ignition key switch 37 is connected with thestarting motor 48 via a relay 310, and the output terminal of thechangeover switch 309 is connected with the coil of the relay 310. Bythis structure, when the switchover circuit 303 is switched to thecontact “a” side according to a failure of the traveling motor 1 whilethe vehicle is stationary, the coil of the relay 310 is supplied withactuating electrical energy so that the relay contact is switched to itscontact “R1” side. As a result, the supply of electricity to thestarting motor 48 is cut, and it is impossible to start the engine 2even if the ignition key switch 37 is turned on.

When, in such a state, the reset switch 36 is actuated, the switchovercircuit 303 is switched to the contact “b” side, and the supply ofelectricity to the coil of the relay 310 is intercepted. The relaycontact is thus switched to the contact “R2” side, which makes possibleto restart the engine 2. It should be noted that it would also bepossible to restart the engine 2, as an alternative to operation of thereset switch 36, by a repairman, etc. using some apparatuses to supplyan external signal of some type. In this manner, it would be impossiblefor an operator to restart the engine upon his own decision.

According to the third embodiment, when a failure of the traveling motor1 is detected, the engine 2 can not be restarted. Therefore, an operatorwill not imprudently restart the engine 2 to drive the vehicle, and itis possible to ensure that he makes an appropriate response to theabnormal operation of the traveling motor 1.

Fourth Embodiment

While, in the first embodiment, the engine speed is limited to theidling rotational speed when a failure of the traveling motor 1 isdetected, regardless of the traveling state or the working state, in thefourth embodiment, no limitation will be imposed upon the engine speedduring the working state. The fourth embodiment of the present inventionwill now be explained with reference to FIGS. 9 and 10. FIG. 9 is acircuit diagram showing the structure of a wheeled hydraulic excavatorequipped with a failure detection device according to the fourthembodiment, and FIG. 10 schematically illustrates details of acontroller 30C according to the fourth embodiment. It should be notedthat the same reference numerals are used for elements similar to thatof FIGS. 1 and 3, and the explanations will focus on the pointsdifferent therefrom.

As shown in FIG. 9, a forward/reverse changing switch 49 for outputtinga switching command to the forward/reverse switchover valve 25, and abrake switch 50 for outputting an operate command to a work brake notshown in the figures are also connected to the controller 30C. As shownin FIG. 10, a switchover circuit 311 is connected with the terminal Q ofthe flip-flop 302, and the switchover circuit 311 is switched accordingto a signal from a work detection section 312. The signals from theforward/reverse changing switch 49 and the brake switch 50 are input tothe work detection section 312. The work detection section 312 sets theswitchover circuit 311 to the contact “a” side when the forward/reverseswitchover valve 25 is in the neutral position and also the work brakeis being operated, while in other conditions, the switchover circuit 311is switched to the contact “b” side.

In other words, the switchover circuit 311 is switched to the contact“b” in any conditions other than the working state, and the switchovercircuits 303 and 305 are switched to the contact “a” side if a failureof the traveling motor 1 occurs, to restrict the engine speed to theidling rotational speed Ni. When, in such a condition, theforward/reverse switchover valve 25 is set to the neutral position inresponse to the operation of the forward/reverse changing switch 49, andalso the work brake is operated by the operation of the brake switch 50,the switchover circuit 311 is then switched to the contact “a” side. Asa result, the switchover circuits 303 and 305 are both switched to thecontact “b” side to cancel the restriction of the engine speed.

According to the fourth embodiment, it is detected as to whether or notthe vehicle has started the work operation according to actuation of theforward/reverse changing switch 49 and the brake switch 50. It ispossible to continue working in the normal manner even when thetraveling motor 1 has broken down since the restriction on the enginespeed is disabled during working. It should be noted that the fourthembodiment can be applied, not only to a system which restricts theengine speed during a failure of the traveling motor 1, but also, in thesame manner, to systems which control the vehicle traveling in otherways, such as by stopping the vehicle traveling, by preventing theengine from restarting, or by causing the parking brake to operate. Inother words, the above restrictions upon traveling may be cancelledduring working.

It would also be possible for the fluid level sensor 35 to beimplemented, not as a switch, but as a sensor which detects the fluidlevel continuously and outputs a set signal to the flip-flop 302 whenthe oil level exceeds the predefined value La. Moreover, although in theabove described embodiments, the buzzer sound is emitted along with theillumination of the warning lamp 40 when the traveling motor 1 hasbroken down, it would also be acceptable to provide one of the warningdevices. Furthermore, it would be possible to flash the hazard warninglamps which are provided around the vehicle, in order to arouse theattention around the vehicle. Although, upon a failure of the travelingmotor 1, the provision of warning and the restriction of the vehicletraveling have been performed at the same time, it would also beacceptable to perform only one of them. Moreover, although the drivingof the traveling motor 1 is limited during a failure of the travelingmotor 1, driving of other actuators, such as a swing motor, may as wellbe restricted.

INDUSTRIAL APPLICABILITY

While a failure detection device for a hydraulic motor has beenexplained in terms of application to a wheeled hydraulic excavator byway of example, it would also be possible, in the same manner, to applythe failure detection device of the hydraulic motor according to thepresent invention to a crawler hydraulic excavator, or to other kinds ofhydraulic drive vehicles.

1. A failure detection device for a hydraulic motor, comprising: ahydraulic pump that is driven by a prime mover; a hydraulic motor fortraveling that is driven by hydraulic oil discharged from the hydraulicpump; a transmission that is connected with an output shaft of thehydraulic motor for traveling; a stopping detection device that detectsthat a traveling vehicle has stopped by detecting a vehicle speed; afluid level detection device that detects an oil level in thetransmission; and a warning device that issues a warning when thestopping detection device detects that the traveling vehicle hasstopped, with supply of the hydraulic oil to the hydraulic motor fortraveling being interrupted, and also the fluid level detection devicedetects that the oil level in the transmission has risen to apredetermined value or greater.
 2. A failure detection device for ahydraulic motor, comprising: a hydraulic pump that is driven by a primemover; a hydraulic motor for traveling that is driven by hydraulic oildischarged from the hydraulic pump; a transmission that is connectedwith an output shaft of the hydraulic motor for traveling; a stoppingdetection device that detects that a traveling vehicle has stopped bydetecting a vehicle speed; a fluid level detection device that detectsan oil level in the transmission; and a drive restriction device thatrestricts a driving of the hydraulic motor for traveling when thestopping detection device detects that the traveling vehicle hasstopped, with supply of the hydraulic oil to the hydraulic motor fortraveling being interrupted, and also the fluid level detection devicedetects that the oil level in the transmission has risen to apredetermined value or greater.
 3. A failure detection device for ahydraulic motor according to claim 2, wherein: the drive restrictiondevice is a rotational speed restriction device that restricts arotational speed of the prime mover, and the rotational speedrestriction device lowers the rotational speed of the prime mover to apredetermined rotational speed when the stopping detection devicedetects that the traveling vehicle has stopped, and also the fluid leveldetection device detects that the oil level in the transmission hasrisen to the predetermined value or greater.
 4. A failure detectiondevice for a hydraulic motor according to claim 2, wherein: the driverestriction device is a traveling prevention device that prevents thedriving of the hydraulic motor for traveling, and the travelingprevention device prevents the hydraulic motor for traveling from beingdriven when the stopping detection device detects that the travelingvehicle has stopped, and also the fluid level detection device detectsthat the oil level in the transmission has risen to the predeterminedvalue or greater.
 5. A failure detection device for a hydraulic motor,comprising: a hydraulic pump that is driven by a prime mover; ahydraulic motor for traveling that is driven by hydraulic oil dischargedfrom the hydraulic pump; a transmission that is connected with an outputshaft of the hydraulic motor for traveling; a stopping detection devicethat detects that a traveling vehicle has stopped by detecting a vehiclespeed; a fluid level detection device that detects an oil level in thetransmission; and a restart prevention device that prevents a restartingof the prime mover when the stopping detection device detects that thetraveling vehicle has stopped, with supply of the hydraulic oil to thehydraulic motor for traveling being interrupted, and also the fluidlevel detection device detects that the oil level in the transmissionhas risen to a predetermined value or greater.
 6. A failure detectiondevice for a hydraulic motor according to claim 2, further comprising: awarning device that issues a warning when the stopping detection devicedetects that the traveling vehicle has stopped, with supply of thehydraulic oil to the hydraulic motor for traveling being interrupted,and also the fluid level detection device detects that the oil level inthe transmission has risen to the predetermined value or greater.
 7. Afailure detection device for a hydraulic motor according to claim 5,further comprising: a warning device that issues a warning when thestopping detection device detects that the traveling vehicle hasstopped, with supply of the hydraulic oil to the hydraulic motor fortraveling being interrupted, and also the fluid level detection devicedetects that the oil level in the transmission has risen to thepredetermined value or greater.
 8. A failure detection device for ahydraulic motor according to claim 1, further comprising: a workingdetection device that detects a working state, and a warning controldevice that disables the warning device from issuing the warning, whenthe working detection device detects the working state.
 9. A failuredetection device for a hydraulic motor according to claim 2, furthercomprising: a working detection device that detects a working state, anda drive restriction control device that disables a drive restriction onthe hydraulic motor for traveling by the drive restriction device, whenthe working detection device detects the working state.
 10. A failuredetection device for a hydraulic motor according to claim 5, furthercomprising: a working detection device that detects a working state, anda restart prevention control device that disables a restart preventionfor the prime mover by the restart prevention device, when the workingdetection device detects the working state.
 11. A failure detectiondevice for a hydraulic motor according to claim 1, further comprising: areset command switch that resets the warning device.
 12. A failuredetection device for a hydraulic motor according to claim 2, furthercomprising: a reset command switch that resets the drive restrictiondevice.
 13. A failure detection device for a hydraulic motor accordingto claim 5, further comprising: a reset command switch that resets therestart prevention device.
 14. A failure detection device for ahydraulic motor according to claim 1, wherein: the warning device isreset by actuation of an ignition key switch.
 15. A failure detectiondevice for a hydraulic motor according to claim 2, wherein: the driverestriction device is reset by actuation of an ignition key switch. 16.A failure detection device for a hydraulic motor according to claim 5,wherein: the restart prevention device is reset by actuation of anignition key switch.
 17. A hydraulic drive vehicle, comprising: ahydraulic pump that is driven by a prime mover; a hydraulic motor fortraveling that is driven by hydraulic oil discharged from the hydraulicpump; a transmission that is connected with an output shaft of thehydraulic motor for traveling; a stopping detection device that detectsthat the vehicle has stopped by detecting a vehicle speed; a fluid leveldetection device that detects an oil level in the transmission; and awarning device that issues a warning when the stopping detection devicedetects that the vehicle has stopped, with supply of the hydraulic oilto the hydraulic motor for traveling being interrupted, and also thefluid level detection device detects that the oil level in thetransmission has risen to a predetermined value or greater.
 18. Ahydraulic drive vehicle, comprising: a hydraulic pump that is driven bya prime mover; a hydraulic motor for traveling that is driven byhydraulic oil discharged from the hydraulic pump; a transmission that isconnected with an output shaft of the hydraulic motor for traveling; astopping detection device that detects that the vehicle has stopped bydetecting a vehicle speed; a fluid level detection device that detectsan oil level in the transmission; and a drive restriction device thatrestricts a driving of the hydraulic motor for traveling when thestopping detection device detects that the vehicle has stopped, withsupply of the hydraulic oil to the hydraulic motor for traveling beinginterrupted, and the fluid level detection device detects that the oillevel in the transmission has risen to a predetermined value or greater.19. A hydraulic drive vehicle, comprising: a hydraulic pump that isdriven by a prime mover; a hydraulic motor for traveling that is drivenby hydraulic oil discharged from the hydraulic pump; a transmission thatis connected with an output shaft of the hydraulic motor for traveling;a stopping detection device that detects that the vehicle has stopped bydetecting a vehicle speed; a fluid level detection device that detectsan oil level in the transmission; and a restart prevention device thatprevents the prime mover from restarting when the stopping detectiondevice detects that the vehicle has stopped, with supply of thehydraulic oil to the hydraulic motor for traveling being interrupted,and also that the fluid level detection device detects that the oillevel in the transmission has risen to a predetermined value or greater.